In Intermediate Frequency (IF) digitization receivers, digitization is typically performed by bandpass sigma-delta modulators (BP ΣΔMs). BP ΣΔMs can be realized in both discrete- and continuous-time (DT and CT) domains. DT BP ΣΔMs refer to the ΣΔMs implemented using switched-capacitor (SC) loop filters, while CT BP ΣΔMs are realized using active-RC, transconductor-C (Gm-C) or LC filter.
DT BP ΣΔMs realized using switch-capacitor circuits cannot operate at high speed, while the CT BP ΣΔMs based on active-RC, Gm-C and LC filters suffer from process and temperature variation (PTV) and cannot achieve satisfactory performance, especially when implemented in CMOS/BiCMOS process.
Further, although some CT BP ΣΔMs have achieved reasonably good performance at high IF, they are implemented in costly III-V processes and consume significant power as seen in the CT BP ΣΔMs disclosed in “High Dynamic Range InP HBT Delta-Sigma Analog-to-Digital Converters,” IEEE Journal of Solid-State Circuits, Vol. 38, No. 9, pp. 1524-1532, September 2003 ” by M. Inerfield, et al. and “IF-Sampling Fourth-Order Bandpass ΣΔ Modulator for Digital Receiver Applications,” IEEE Journal of Solid-State Circuits, Vol. 39, No. 10, pp. 1633-1639, October 2004″ by A. E. Cosand, et al. High-performance CT BP ΣΔMs in CMOS/BiCMOS technology at high IF have yet to materialize.
BP ΣΔMs based on electromechanical resonators have been proposed recently in [Y. P. Xu, R. Yu, W. T. Hsu and A. R. Brown, “A Silicon Micromechanical Resonator Based CMOS Bandpass Sigma-Delta Modulator,” in Proc. of Asian Solid-State Circuit Conference (A-SSCC'06), November 2006. pp. 143-146; R. Yu, Y.P. Xu, “A 47.3-MHz SAW Resonator Based CMOS Second-Order Bandpass Sigma-Delta Modulator with 54-dB Peak SNDR,” in Proc. IEEE Custom Integrated Circuits Conf. (CICC'05, pp. 203-206, September 2005]. These BP ΣΔMs achieve comparable or better SNDR (Signal to Noise plus Distortion Ratio) performances in narrowband (200 kHz) FM application, but are more suitable for narrowband applications. Although multiple resonators with different center frequencies can be used to achieve a wider passband in a higher-order loop filter, they are difficult to realize in practice due to the increased parasitics and complexity.
Therefore, there exists a need to provide a system and method for a bandpass sigma-delta modulator to address one or more of the problems mentioned above.